As shown in FIG. 1, a conventional axial flow gas turbine engine 10 comprises an air intake 11, a low pressure compressor (or fan) 12, an intermediate pressure compressor 13, a high pressure compressor 14, a combustor 15, a high pressure turbine 16, an intermediate pressure turbine 17, a low pressure turbine 18, and an exhaust nozzle 19.
In operation, air is drawn into the engine 10 through the intake 11 and accelerated by the fan 12, to produce two air flows: a first air flow which enters the intermediate pressure compressor 13 and a second air flow which bypasses the core of the engine to provide direct propulsive thrust.
The first air flow entering the intermediate pressure compressor 13 is compressed before entering the high pressure compressor 14 where further compression takes place.
The compressed air leaving the high pressure compressor 14 is directed into the combustor 15 where it is mixed with fuel and the resulting mixture is combusted. The high pressure combustion products then rapidly expand as they pass through and drive the high, intermediate and low pressure turbines 16, 17 and 18. The gas leaving the low pressure turbine 18 is then exhausted through the exhaust nozzle 19 and provides additional propulsive thrust.
The high, intermediate and low pressure turbines 16, 17 and 18 respectively drive the high and intermediate pressure compressors 14 and 13 and the fan 12 by means of separate interconnecting shafts.
Typical axial-flow compressors and turbines each generally comprise a plurality of stages, each of which in turn comprises a stator stage which is mounted on the casing inner wall and a rotor stage which is rotatably driven in the casing.
Each stator stage will typically comprise a plurality of individual stator vanes arranged as an annular array supported between respective inner and outer supports (or “platforms”), with each individual stator vane extending substantially radially between the platforms. The stator vanes in each stator stage are configured to straighten the air flow before it enters the adjacent rotor stage.
Due to the need to support the compressor and turbine portions of the engine within the engine casing, it is known to use substantial mounting pylons or struts within the engine, for example downstream of the intermediate pressure compressor. These struts can cause disruption to the air flow through the compressor which in turn can cause a circumferential pressure variation around the engine's air intake. This can reduce the efficiency of the engine and may adversely stress the fan and compressor blades.
It is an object of the present invention to provide an improved stator stage which ameliorates the above-mentioned problems, and a method for assembling such a stator stage.